<?php
$user_name = "test";

$a = "hello";
$$a = "world";

// echo $a, $hello;
// echo $$a;

// echo "$a";

$a1 = "test";
// 引用赋值
$b1 = &$a1;
// echo $b1, "<br>", $a1, "<br>"; // test test
$b1 = "2222";
// echo $b1, "<br>", $a1, "<br>";// 2222  2222

// 定义 常量 值 tom
// 变量1的值 hello, 变量1的值 world
// 把上面变量输出，浏览器显示结果 tom: hello world
define("USERNAME", "tom");
$say1 = "hello";
$say2 = "world";

echo USERNAME, ": ", $say1, "&nbsp;",$say2;

?>